1. Field of the Invention
The disclosed invention generally relates to an electrical junction box or outlet box construction. More particularly, the disclosed invention relates to a so-called Chicago style plenum type electrical junction box, which boxes provide air impermeable barriers for routing conductors, and which box according to the present invention provides air impermeable fastener knockouts for easing installation.
2. Description of the Prior Art
The prior art discloses a variety of outlet boxes or electrical junction boxes and the like. Some of the more pertinent prior art relating to junction boxes are described hereinafter. U.S. Pat. No. 2,092,367 ('367 Patent), which issued to Breitenstein, for example, discloses an Outlet Box. The '367 Patent describes an outlet box made of any suitable metal, such as steel, and comprises a horizontal wall or base and integral side and end walls. The base and walls may be provided with a plurality of knock-outs for the reception of conduits, cables or conductors leading to the interior of the box. The outlet box may also be provided with openings for fastening the box to the rafters, studs, or other supporting members and for securing the barrier wall in position. The side and end walls may be provided with inturned tongues or flanges for the reception of threaded fastening means for fastening a cover plate to the open face of the box. The cover plate is made in variable depths or thicknesses determinable upon the type of construction with which the box is used.
U.S. Pat. No. 2,324,155 ('155 Patent) which issued to Haynes, discloses an Outlet Box. The '155 Patent describes an outlet box, made of any preferred material, and comprises as constituent portions, a disk-like head having ventilating openings and a rim connected to the head and supplied with any suitable attaching means. Disks results from the formation of holes in the head of the box, the constituent material of which is extruded slightly to form oppositely disposed, integral, peripheral lips and oppositely disposed integral, peripheral wings extended between the lips and of the greater area than the lips.
U.S. Pat. No. 2,659,765 ('765 Patent), which issued to Dunn, discloses an Electrical Splice Box. The '765 Patent describes a junction box for electrical circuits, substantially octagonal in shape. It is provided with a plurality of plugs in that these plugs are severed through substantially the entire circumference with the exception of a small tongue or fin. The plugs are embossed, so as to be located substantially entirely within the box. These knock-out plugs are similar to the knock-out plugs now used in conventional Junction and outlet boxes. The periphery of the box is provided with a pair of inwardly directed lugs or tabs having threaded apertures adapted to receive retaining screws threadedly engaging the apertures adapted to receive retaining screws threadably engaging the apertures used in holding a metal plate forming a cover for the junction box. The structure described thus far is conventional, with the exception of a portion of the box.
U.S. Pat. No. 3,349,946 ('946 Patent), which issued to Lee, discloses an Electric Outlet Box. The '946 Patent describes an electric outlet box in which the walls and bottom of the box are provided with one or more circular score lines defining knock-out discs. Each circular score line has spaced apart recesses in the disc portion to provide tongues that extend inwardly into the interior of the box. An anchor sleeve has a cylindrical portion of the same diameter as the circular score line and is provided with longitudinally extending grooves in this portion that receive the tongues. The grooves extend into an integral head of the anchor sleeve and prevent the head from rotating when the tongues are received therein.
U.S. Pat. No. 3,965,287 ('287 Patent), which issued to Mueller, discloses certain Electric Circuit Enclosure Transformer Mounting Means. The '287 Patent describes a mounting plate adapted to mount a transformer on an electric circuit enclosure. The mounting plate is provided with a dual function knockout arrangement so that the transformer to be mounted can either be surface mounted with different types of mounting means, or can be recessed into the plate by the removal of the entire knockout portion.
U.S. Pat. No. 4,051,322 ('322 Patent), which issued to Park et al., discloses an Electrical Junction Box. The '322 Patent describes an electrical junction box comprising a base and a four-sided peripheral wall with a pair of opposite tubular connectors protruding outwardly from opposite end walls and providing ingress through respective walls, into the box. The box is split into two complementary parts along a line passing through the base and the opposite end walls including the connectors. The base is hinged so that the complementary parts may pivot relative to each other from their normal position of abutment to each other to open the connectors so that conductors within a sheathed cable can be passed through the box from the connectors after severing the surrounding sheath but without severing the cable conductors, and the severed ends of the sheath can be connected to the protruding connectors. This permits making electrical connections to the conductors within the box without severing the conductors. This also provides access to the inside of the sheath to fish additional circuits into the junction box.
It will be observed that the split connectors are attached to the end walls and project from them. The end wall parts are shaped to pass the conductors received by the connectors. In the illustrated embodiment they do this by receiving the connector parts themselves, the base flanges being mounted on the inside of the end wall parts. Nails may be driven through the holes in the based of the box to hold the box closed and also to mount it to a base such as a joist or girder. This nailing operation will be done after the conductors are placed in the opened tubes, and will be enclosed in the tubes when the box is closed as shown.
U.S. Pat. No. 4,244,483 ('483 Patent) which issued to Bauer et al. discloses an Electrical Wiring Box. The '483 Patent describes a molded plastic electrical wiring box having knock-out regions comprising a two-flap structure with the flaps having essentially planar offset surfaces providing a frangible bridge or web to separate the flaps.
U.S. Pat. No. 4,316,999 ('999 Patent), which issued to Nattel, discloses an Electrical Wiring Box and Cable Clamp. The '999 Patent describes an electrical wiring box comprising a wiring box with end, side, and rear walls and a cable clamp. The wiring box wall structure is provided with knock-out regions, a first cable-engaging means, and means for attaching the cable clamp to a wall having knock-out regions. The cable clamp comprises a flexible flat sheet, attachable at one end to the box wall structure interior to the box. The opposite end of the cable clamp is provided with a foot portion, formed at an acute dihedral angle with the main body of the clamp. A non-metallic sheathed electrical cable inserted through a knock-out opening in the box wall structure, deflects the unattached end of the clamp inwardly into the box, engaging the cable against removal from the knock-out opening in an outward direction by the action of the first cable-engaging means and the heel of the clamp foot portion bearing oppositely against the cable sheath.
U.S. Pat. No. 4,455,449 ('449 Patent), which issued to Rendel, discloses a Universal High/Low Voltage Kit for Junction Wiring Box. The '449 Patent describes a kit which is installable in a wiring junction box so as to adapt the box to receive high and low voltage wiring from high and low voltage sources and high and low voltage wiring from an appliance, and to permit the connection of the high and low voltage connections within the box being physically separated from one another. The kit comprises a partition installable within the box so as to divide the interior of the box into a high voltage compartment and a low voltage compartment. A cover is provided for closing the open front face of the box, this cover including a first cover plate securable to the box to overlie only a portion of the box bottom. The cover assembly further includes a second cover plate removably installable on the box after the wiring connections have been made within the box thereby to permit inspection of the wiring connections without disturbing the wiring within the box.
U.S. Pat. No. 4,825,339 ('339 Patent), which issued to Boudon et al., discloses a Sheet Metal Knock-Out. The '339 Patent describes a knock-out in the wall of the housing for electronic equipment which is selectively removed to provide a knock-out opening. A wall includes first and second slits positioned along the boundary of the knock-out and separated by a land. The wall includes a break out opening adjacent to each land. Break portions of the wall separate the break out opening from the first and second slits. These break portions are severed to interconnect the first and second slits through the break out opening and permit removal of the knock-out. Plural such slits and break out openings are provided and arranged to provide a knock out of rectangular or other desired geometric shape. The slits and break out openings are sized to provide electromagnetic interference shielding. Also, the break portions are of a length which is approximately no greater than the thickness of the wall and are positioned to facilitate removal of the knock-out without deforming the wall and without leaving burrs in the knock-out opening.
U.S. Pat. No. 5,698,820 ('820 Patent), and U.S. Pat. No. 5,883,332 ('332 Patent), which issued to Collard, disclose Method(s) and Apparatus(es) for Junction Box and Conduit Support. The noted patents describe a flat plate to which an electrical junction box is centrally mounted with the plate extending beyond the sides of the junction box and conduits entering the junction box are supported by conduit clamps attached to the extended portions of the plate. Slots are provided in the extended portions of the flat plate to permit alignment of the conduit clamps with the entering conduit. These disclosures are illustrate standardized fastener hole arrangements.
It may be seen from a consideration of the foregoing that the prior art appears to be silent on a junction box having fastener knockouts for enabling easy removal of knockout structure for creating fastener-receiving apertures and maintaining an otherwise air impermeable barrier. Accordingly, the prior art perceives a need for such a junction box, as described in more detail hereinafter.
It may be seen from a consideration of the general state of the art that standard electrical conduit boxes have trade size knockouts that are cut into the steel side and bottom walls and pushed out being secured to the box body by only a small tab that connects the knockout to the box. Typically, there is a ⅛″-¼″ gap around all knockouts in a standard electrical conduit box. In addition to the conduit knockouts in the side and bottom of the standard electrical conduit box, the conduit box may also have fastener-receiving holes in the side and bottom of the box so the installer can insert a screw or nail through the box hole and mount it to a wood, concrete or steel surface.
So-called Chicago plenum air tight electrical boxes are similar to the standard version electrical conduit box, but the knockouts must be re-hit with the surface body of the box to create an air tight seal. It is also imperative that there are no various sized holes in this box or it would lose its air tight seal. It cannot contain any holes or gaps that are common in standard electrical conduit boxes. Chicago Plenum boxes have been made without mounting holes for more than 50 years by at least 4 different manufacturers. This is a huge inconvenience to the installer because they are forced to take out a power drill and drill mounting holes where they need them. This is very time consuming, power consuming, and costly to the installer.